The turbine section of a gas turbine engine contains a rotor shaft and one or more turbine stages, each having a turbine disc (or rotor) mounted or otherwise carried by the shaft and turbine blades mounted to and radially extending from the periphery of the disc. A turbine assembly typically generates rotating shaft power by expanding hot compressed gas produced by the combustion of a fuel. Gas turbine buckets or blades generally have an airfoil shape designed to convert the thermal and kinetic energy of the flow path gases into mechanical rotation of the rotor.
Turbine discs are exposed to very high temperatures at the disc post or rim (where blades are attached) due to contact with the hot compressed gas and are exposed to low temperatures at the bores (where the disc is carried by the shaft). The variation of temperatures across the discs is referred to as the rim-to-bore temperature gradient. Conventional coatings for discs reduce the life of the discs as the rim-to-bore gradient increases due to isolation created by the coating. Unless the coating is metallic, which adds weight to the disc or creates galvanic pairs, conventional coatings for discs do not directly conduct heat but prevent heat conduction. Discs are thus typically uncoated and have a lifetime limited by the rim-to-bore temperature gradient. The surrounding temperatures and traces of hot gas ingestion from imperfect purging also reduce the life of the discs by reducing the disc's damage tolerance.
Accordingly, there remains a need for an improved design for discs and methods of making such discs to reduce rim-to-bore gradients and improve the lifetime of the discs.